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| Titel |
Constraining nitrogen cycling hotspots in contaminated aquifers |
| VerfasserIn |
Naomi Wells, Kay Knoeller |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096287
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| Publikation (Nr.) |
 EGU/EGU2014-11785.pdf |
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| Zusammenfassung |
| Accurate assessments of the fate of inorganic nitrogen (N) in groundwater are needed in order
to mitigate the threat that ammonium (NH4+) and nitrate (NO3-) pose to water quality and
the long-term health of down-gradient ecosystems. However, such assessments are currently
limited by difficulties in measuring the biological attenuation (via either denitrification or
anaerobic ammonia oxidation (anammox)) of these reactive species in-situ. Based on the
knowledge that both of these processes can create unique fractionation patterns
in the residual N pools, the objective of this research was to build a template for
identifying and quantifying N removal hotspots within complex aquifers using
isofluxes. The variations in concentration and isotopic abundance of multiple dissolved
inorganic N species (δ15N of NH4+, and δ15N and δ18O of NO2- and NO3-) were
measured in 100 wells across two contaminated megasites in Western Europe. The
sampling locations were selected span the NH4+ (the dominant N form in both
sites) concentration gradient (0 to 900 mg NH4+-N l-1) over depth and distance,
which coincided with gradients in co-contaminants BTEX and sulphate of 0 to 5 mg
l-1 4 to 11000 mg l-1, respectively. Although NO2- is a key component of both
anaerobic and aerobic ammonium oxidation, it is rarely detected in groundwater.
Yet, by analysing for it on-site, we found that NO2- concentrations reached up to
0.7 mg NO2-N l-1 and had a highly sensitive isotopic composition (mean of -5
±23o(δ15N) and +11 ±12o(δ18O)). The largest NO2- concentrations coincided with
those of NH4+ levels, meaning that attenuation fluxes could be partitioned between
anammox and denitrification using simple isotope mass balance calculations based on
Rayleigh type isotope fractionation and established nitrate (δ15N and δ18O) isotope
dynamics during denitrification. The constraints on N attenuation within these complex
hydrological and chemical setting created by overlaying isoflux maps for each N species
provide a template for a new means of assessing a site’s in-situ remediation capacity. |
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